Preparation of organic carboxylic acid esters of cellulose



Patented Mar. 9, 1954 PREPARATION OF ORGANIC CARBOXYLIC ACID ESTERS OF CELLULOSE Mark Plunguian, Gillette, N. J assignor to Gelanese Corporation of America, New York, N. Y., a corporation of Delaware N Drawing. Application December 19, 1950, I

Serial No. 201,694

This invention relates to organic acid esters of cellulose and relates more particularly to an improved process for the production of organic acid esters of cellulose from cellulosic material derived from wood.

In accordance with one process for the production of organic acid esters of cellulose, a cellulosic material is first pretreated, in one or more stages, with a lower aliphatic acid and, if desired, with an esterification catalyst to increase its reactivity, and the pretreated cellulosic material is then esterified with an organic acid anhydride. When organic acid esters of cellulose are produced in this manner from cellulosic material derived from wood, it has heretofore been the practice to employ for this purpose a specially purified wood pulp, commonly known as an acetate pulp, substantially free from hemicelluloses and other impurities and containing more than about 94% by weight of alpha-cellulose. If an attempt is made to prepare organic acid esters of cellulose from a less highly purified wood pulp containing a relatively high proportion of hemicelluloses and a relatively low proportion of alpha-cellulose, there is obtained an unsatisfactory product of poor color, clarity and filtering properties. In addition, solutions of the organic acid ester of cellulose prepared from the less highly purified wood pulp exhibit a very rapid increase in viscosity as the concentration thereof i raised. As a result, it is difficult to prepare and handle the said solutions in concentrations sufficiently high to be useful in the spinning of filamentary materials and for other commercial purposes. Although the less highly purified wood pulps are considerably less expensive than the acetate pulps, the unsatisfactory properties of the organic acid esters of cellulose prepared therefrom has hitherto substantially prevented their use for the production of these materials.

It is an important object of this invention to provide a process for the production of organic acid esters of cellulose from cellulosic material derived from wood which will be free from the foregoing and other disadvantages of the processes hitherto used for this purpose.

Another object of this invention is to provide a process for the production of organic acid esters of cellulose from cellulosic material derived from wood in which there may be employed wood pulps having a relatively high proportion of hemicelluloses and a relatively low content of alpha cellulose.

Other objects of this invention will b apparent from the following detailed description and claims.

Claims. (Cl. 260-229) I have now discovered that organic acid esters of cellulose having satisfactory properties may be prepared from wood pulps having a relatively high proportion of hemicelluloses and a relatively low content of alpha cellulose if said cellulosic materials are treated, during the pretreatment process, with formaldehyde as well as with a lower aliphatic acid. Thus, in accordance with the present invention, a cellulosic material derived from wood and having more than about 10% by weight of hemicelluloses and less than about by Weight of alpha cellulose is pretreated, in one or more stages, with formaldehyde and a lower aliphatic acid, and, if desired, with an esterification catalyst. The pretreated cellulosic material is then esterified with an organic acid anhydride. Following the esterification, the organic acid ester of cellulose may be ripened to reduce its acetyl content to the desired value, precipitated, washed, stabilized and washed again, all in accordance with methods well known in the art. The organic acid esters of cellulose prepared in accordance with this process are of good color, clarity and filtering properties. In addition, they form highly concentrated solutions of relatively low viscosity so that they may be readily employed in the spinning of filamentary materials and for other commercial purposes.

The formaldehyde may be applied to the cellulosic material at any stage of the pretreatment process either together with, before, or after the pretreatment of said cellulosic material with a lower aliphatic acid. Advantageously, however, the formaldehyde is applied to the cellulosic material together with the lower aliphatic acid to reduce the number of steps in the pretreatment process to a minimum. The pretreatment of the cellulosic material with formaldehyde is carried out at a temperature of less than about 45 0., and preferably at a temperature of between about 20 and 30 C. for a period of between about and 3 hours, employing from about 2 to 20 parts by Weight of formaldehyde basis) for each 100 parts by weight of cellulosic material. The greater the amount of formaldehyde and the higher the temperature employed during the pretreatment, the shorter will be the time required to complete the said pretreatment.

The formaldehyde may be employed in aqueous solution, but is preferably employed in solution in the lower aliphatic acid with which the cellulosic material is pretreated. Instead of employing formaldehyde itself, there may be employed substances which will liberate formaldehyde during the pretreatment such as, for example, paraformaldehyde.

Suitable lower aliphatic acids that may be employed in pretreating the cellulosic material include, for example, formic, acetic, .propionic and butyric acids, as well as mixtures thereof. There may be employed, for the pretreatment, from about 200 to 350 parts by weight of the lower aliphatic acid for each 100 parts by weight of the cellulosic material. The cellulosic material may also be pretreated with an esterification catalyst such as, for example, sulfuric acid, in an amount of from about 3 to 15 parts by weight for each 100 parts by weight of the cellulosic material.

Wood pulps that may be employed for the production of organic acid esters of cellulose in accordance with the present invention include, for example, sulfie pulps, sulfate pulps or soda pulps, which pulps may have .been subjected to a suitable purification process, .but which still have a relatively high proportion of 'hemicelluloses and a relatively low proportion of alpha cellulose.

Ihe pretreatment of the cellulosic material may, if desired, be carried out in a plurality of stages as disclosed in Seymour et al., application Ser. No. 58,028,.filed November 2, 1948, now Patent No. 2,503,634.

Starting with a wood pulp containing a relatively high proportion of .hemicelluloses, the process of the present invention produces an organic acid ester of cellulose which has a significantly lower content of hemicelluloses than the starting material, indicating that the formaldehyde pretreatment in some way causes the elimination of said .hemicelluloses during the production .of the organic acid ester of cellulose.

The process of the present invention will now be described specifically in connection with the production of cellulose acetate, which is commercially the most important organic acid ester of cellulose at the present time. It is to .be understood, however, that it is also applicable to the production of other organic acid esters of cellulose, including the lower aliphatic acid esters of cellulose, such as cellulose propionate, cellulose butyrate, cellulose acetate propionate and cellulose acetate butyrate, as well as to the production of cellulose acetate crotonate, cellulose acetate stearate and the vbenzoic acid ester of cellulose.

The following examples are given to illustrate this invention further.

Example I A paper type sulfite wood pulp having an alpha cellulose content of 87.5% and a hemicellulose content of 12.5% including a non-glucosidic hemicellulose content of 6.0% mannan and 5.5% xylan is treated at a temperature of 28 C. for 2% hours with a solution containing 315 parts by weight of acetic acid, 17 parts by weight of formaldehyde (as paraform) and 14 parts by weight of sulfuric acid for each 100 parts by weight of pulp. The pretreated pulp is then esterified with acetic anhydride, and the cellulose acetate formed is ripened, precipitated and washed in a manner well known in the art.

The ripened cellulose acetate, containing 0.8% bound formaldehyde, is obtained in a yield of 152% based on the cellulose and has a non-glucosidic heinicellulose content, based -on the cellulose, of 2.3% mannan and 71.5% vxylan. A 27 by weight solution of this cellulose acetate in acetone has a viscosity of 1000 poises. This cellulose acetate :has an intrinsic viscosity of 1.63

and spins readily to form filaments having a tenacity of 1.25 grams per denier and an elongation of 29.2% at the breaking point. The cellulose acetate is also clear, colorless and exhibits good filtering properties.

A ripened cellulose acetate prepared from the same wood pulp, omitting the formaldehyde pretreatment, but making no other changes in the process, is obtained in a yield of 158.6% based on :the cellulose and has a non-glucosidic hemicellulose content, based on the cellulose, of 5.4% mannanand 4.0% xylan. A 27% by weight solution of this cellulose acetate in acetone has a viscosity of 9,500 poises which is too high for successful spinning by commercial methods; the intrinsic viscosity of this cellulose acetate is 1.82. When spun from a 20.3% by weight solution in acetone having a viscosity of 1090 poises it yields filaments having a tenacity of only 1.07 grams per denier and an elongation of 28.8% at the breaking point. The cellulose acetate has poor color, clarity and Ifiltering properties.

Example II An unpurified sulfite woodpulp having an alpha cellulose content of 86.5% and a hemicellulose content of 13.5 including anon-glucosidic hemicellulose content of 6.1% mannan and.2.7% xylan is treated at 25 C. for 1 hour with a solution containing 315 parts :by weight of acetic acid, 17 parts by weight of formaldehyde (as parafor-m) and 14 by weight of sulfuric acid for each 10.0 parts by weight of pulp. The pretreated pulp is then esterified with acetic anhydride and the cellulose acetate formed is ripened, precipitated and washed-inamanner well known the art.

The ripened cellulose acetate, containing 1.0% combined formaldehyde, has a 3.2% mannan contentbased on the cellulose. A.27% by weight solution-of this cellulose acetate in acetone has .a viscosity of 4,000 poises andspins readily to form filaments having a tenacity of 1.32 grams per denier and an elongation of 26.6% at the breaking point. The cellulose acetate is clear, colorless and has good filtering properties.

A ripened cellulose acetate prepared from the same wood pulp, omitting the formaldehyde pre treatment, but making no other changes in the process, has a mannan content of 4.7 based on the cellulose. A 27% by weight solution of this cellulose acetate in acetone has a viscosity of 32,000 poises which is too high for spinning by commercial methods. When spun from a more dilute solution it "yields filaments having a tenacity of 1.17 grams per denier and an elongation of 27.5% at the breaking point. The cellulose acetate has poor color, clarity andfiltering properties.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that .many variations may be made therein without departing from the spirit of my invention.

Having described my invention, what I desire to secure by Letters Patent is:

1. in process for the production of organic acid esters of cellulose from cellulosic material having a relatively high content of heznicelluloses, the steps which comprise pretreating said cellulosic material with formaldehyde while maintaining a temperature of less than about 45 C. throughout the pretreatment with formaldehydeend esterifying the pretreatedcellulosic material with an organic carboxylic acid anhydride.

2. In a process for the production of organic acid esters of cellulose from cellulosic material having a relatively high content of hemicelluloses, the steps which comprise pretreating said cellulosic material with formaldehyde and a lower aliphatic acid while maintaining a temperature of less than about 45 C. throughout the pretreatment with formaldehyde, and esterifying the pretreated cellulosic material with an organic carboxylic acid anhydride.

3. In a process for the production of organic acid esters of cellulose from cellulosic material having a relatively high content of hemicelluloses, the steps which comprise pretreating said cellulosic material with from about 2 to 20 parts by weight of formaldehyde for each 100 parts by weight of the cellulosic material while maintaining a temperature of less than about 45 0. throughout the pretreatment with formaldehyde, and esterifying the pretreated cellulosic material with an organic carboxylic acid anhydride.

4. In a process for the production of organic acid esters of cellulose from cellulosic material derived from wood and having less than about 90% of alpha cellulose and more than about of hemicelluloses, the steps which comprise pretreating said cellulosic material with formaldehyde at a temperature of between about and 45 C., the temperature being maintained below 45 C. throughout the pretreatment with formaldehyde and esterifying the pretreated cellulosic material with an organic carboxylic acid anhydride.

5. In a process for the production of organic acid esters of cellulose from cellulosic material derived from wood and having less than about 90% of alpha cellulose and more than about 10% of hemicelluloses, the steps which comprise pretreating said cellulosic material with formaldehyde, a lower aliphatic acid and an esterification catalyst at a temperature of between about 20 and 45 C., and esterifying the pretreated cellulosic material with an organic carboxylic acid anhydride.

6. In a process for the production of organic acid esters of cellulose from cellulosic material derived from wood and having less than about 90% of alpha cellulose and more than about 10% of hemicelluloses, the steps which comprise pretreating said cellulosic material with from about 2 to 20 parts by weight of formaldehyde and from about 200 to 350 parts by weight of a lower aliphatic acid for each 100 parts by weight of the cellulosic material at a temperature of between about 20' and 45 C., the temperature being maintained below 45 C. throughout the pretreatment with formaldehyde and esterifying the pretreated cellulosic material with an organic carboxylic acid anhydride.

7. In a process for the production of organic acid esters of cellulose from cellulosic material derived from wood and having less than about 90% of alpha cellulose and more than about 10% of hemicelluloses, the steps which comprise simultaneously pretreating said cellulosic material with from about 2 to 20 parts by weight of formaldehyde, from about 200 to 350 parts by weight of a lower aliphatic acid and from about 5 to 15 parts by weight of an esterification catalyst for each 100 parts by weight of the cellulosic material for a period of between about and 3 hours at a temperature of between about 20 and 45 C., and esterifying the pretreated cellulosic material with an organic monocarboxylic acid anhydride.

8. In a process for the production of cellulose acetate from cellulosic material derived from wood and having less than about 99% of alpha cellulose and more than about 10% of hemicelluloses, the steps which comprise pretreating said cellulosic material with formaldehyde while maintaining a temperature of less than about 45 C. throughout the pretreatment with formaldehyde, and esterifying the pretreated cellulosic material with acetic anhydride.

9. In a process for the production of cellulose acetate from cellulosic material derived from wood and having less than about of alpha cellulose and more than about 10% of hemicelluloses, the steps which comprise simultaneously pretreating said cellulosic material with from about 2 to 20 parts by weight of formaldehyde and from about 200 to 350 parts by weight of a lower aliphatic acid for each 100 parts by weight of cellulosic material and with an esterification catalyst for a period of between about T and 3 hours at a temperature of between about 20 and 45 C., and esterifying the pretreated cellulosic material with acetic anhydride.

10. In a process for the production of cellulose acetate from cellulosic material derived from wood and having less than about 90% of alpha cellulose and more than about 10% of hemicelluloses, the steps which comprise simultaneously pretreating said cellulosic material with from about 2 to 20 parts by weight of formaldehyde, from about 200 to 350 parts by weight of acetic acid, and from about 3 to 15 parts by weight of sulfuric acid for each 100 parts by weight of cellulosic material for a period of between about 1 6 and 3 hours at a temperature of between about 20 and 45 C., and esterifying the pretreated cellulosic material with acetic anhydride.

MARK PLUNGUIAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,445,382 Zdanowich Feb. 13, 1923 1,930,145 Murray et al. Oct. 10, 1933 2,243,765 Morton May 27, 1941 2,298,260 Kantorowicz Oct. 6, 1942 2,315,973 Malm Apr. 6, 1943 2,400,361 Malm et a1 May 14, 1946 2,478,383 Fordyce et al Aug. 9, 1949 2,478,425 Richter et a1 Aug. 9, 1949 2,487,892 Richter et a1 Nov. 15, 1949 

1. IN A PROCESS FOR THE PRODUCTION OF ORGANIC ACID ESTERS OF CELLULOSE FROM CELLULOSIC MATERIAL HAVING RELATIVELY HIGH CONTENT OF HEMICELLULOSES, THE STEPS WHICH COMPRISE PRETREATING SAID CELLULOSIC MATERIAL WITH FORMALDEHYDE WHILE MAINTAINING A TEMPERATURE OF LESS THAN ABOUT 45* C. THROUGHOUT THE PRETREATMENT WITH FORMALDEHYDE, AND ESTERIFYING THE PRETREATED CELLULOSIC MATERIAL WITH AN ORGANIC CARBOXYLIC ACID ANHYDRIDE. 